Thermal properties and tempurature Flashcards
What is thermal expansion and why does it occur
Thermal expansion - when materials are heated, they expand
This occurs because the molecules gain K.E. and start to move around which causes them to spread out (hence expansion)
What state expands the most and which expands the least
The most expansion - gas
The least expansion - solid
Why does gas expand the most but solid the least
Gases expand the most due to there being no bonds holding the molecules together;
whereas solids only expand slightly due to there being strong bonds holding the molecules together
Example of everyday use of thermal expansion
Bimetallic strip in a temperature-activated switch - a metal bar made up of two metals with different rates of expansion
When a bi-metallic strip is heated what happens
The two metals expand at different rates causing the bar to bend.
What could happen to solid materials when they expand, how can this be stopped
Solids can buckle if they expand too much
To prevent this, gaps are built in between, providing room for expansion.
What happens when a substance is heated,
give examples of the things that change
Its physical properties can change
e.g. density and volume
electrical resistance
If these properties change in a well defined way, then you can determine the temperature
What is a fixed point
A tempurature where an easily identifiable change occurs
How do you build a thermometer
Find out two fixed points on thermometer - 0C (m.p.) and 100C (b.p.)
Equally distribute values between two points using a ruler
Describe experiment to show gases expand more than solids
Measure volume of both states at room temperature
Add heat equally to both using water bath
When they are of equal temperature increase
You should expect to see gases expand more than the solid
How is linearity achieved in a liquid-in-glass thermometer
Have a tube of uniform diameter
Define “linearity” in a thermometer
Getting the same change in length/*C
Define “sensitivity”
Change of input/ change in output
How much longer does the column of liquid get/*C of temp increase
Define “range”
The lowest and highest temperature readings on the thermometer
What is contained in a liquid in glass thermometer
A thin glass capillary tube containing a liquid that expands with temperature
At one end there is a glass bulb, containing a larger volume of the expanding liquid which moves into the capillary tube
Why is the capillary tube narrow
So that when the volume expands/contracts by a small percentage there is still a visible change
How can sensitivity be increased in a liquid glass thermometer
By using a liquid with a greater co-efficient of expansion
What does increasing the size of the bulb do to sensitivity
It increases the sensitivity, but if it is too large it will cause response time to be low as the liquid would take a long time to heat up
What is a thermocouple?
A thermocouple is two different types of wire attached together
When the wires are heated, a potential difference occurs
The greater the temperature, the greater the potential difference
How does a thermocouple measure tempurature
When the thermal energy increases, the potential difference increases
This is read by looking at a heat-current graph
What increases when a substance is heated
Its internal energy increases
the higher the tempurature, the more thermal energy
What two energy types are contained in a substance
Kinetic energy - due to the molecules random motion
Potential energy - due to the bonds between the molecules
What is the thermal capacity of an object
The required amount of energy to raise the tempurature of a substance by 1*C
This amount of energy is also equal to the amount given out when the substance is cooled by 1*C
The greater the thermal capacity of an object…
The more energy it requires to raise its’ tempurature by 1*C
Equation for thermal capacity
C = mc
= mass x specific heat capacity
g x j/kg*C
Equation for the change in energy
= Mass x Specific heat capacity x Change in tempurature
mc x change in T
Give an experiment to measure the specific heat capacity of a substance
- ) Place a beaker on a balance and press zero
- ) Add oil to the beaker and measure its mass
- ) Read the starting temperature of the oil
- ) Connect a joulemeter to the immersion heater
- ) Time for 30 minutes
- ) Read off the number of joules passed through the immersion heater
- ) Read the final temperature of the oil
- ) Use the equation - E = MCΔT
While a substance changes state why does the temperature remain constant
Because the energy is used to break bonds of the molecules rather than increase its K.E.
What is the difference between boiling and evaporation
Boiling occurs at a fixed tempurature and occurs throughout the liquid
Evaporation can occur at any temperature and occurs at the surface of the liquid
What is latent heat
The required amount of energy to change to state of a substance
This energy is required to break bonds holding molecules together
What is latent heat of fusion
The required energy to change a solid into a liquid
What is latent heat of vaporization
The required energy to change a liquid into a gas
Equation for latent heat
E = ml
Definition of melting point
The tempurature at which a solid changes into a liquid
Definition of boiling point
The tempurature at which a liquid changes into a gas
Describe an experiment to determine the latent heat of water
Use electrical heater to melt ice for 5 minutes
The electrical energy used is calculated by multiplying the power of electrical heater by time
The mass of water melted is recorded, and the relationship between energy input and mass is calculated
The latent heat is determined by using the equation E=ml
